Surface acoustic wave devices

ABSTRACT

A surface acoustic wave device has a supporting substrate, a propagation substrate made of a piezoelectric single crystal, an organic adhesive layer having a thickness of 0.1 to 1.0 μm and bonding the supporting substrate and the propagation substrate, and a surface acoustic wave filter provided on the propagation substrate.

FIELD OF THE INVENTION

The present invention relates to a surface acoustic wave device withsuperior temperature characteristics of frequency.

BACKGROUND OF THE INVENTION

Surface acoustic wave (SAW) devices have been in extensive use asbandpass filters in communication equipments such as a cellular phoneand the like. With the enhancement of the performance of cellular phoneand the like, there is an increasing demand to enhance the performanceof the filters using the surface acoustic wave devices.

In the surface acoustic wave device, however, there is a problem of thepassband shifts due to temperature changes. In particular, lithiumniobate and lithium tantalate frequently used have highelectromechanical coupling coefficients, and thus provide an advantagein achieving broad-band filtering characteristics. However, lithiumniobate and lithium tantalite are of inferior temperature stability.

For example, in lithium tantalate, the temperature coefficient offrequency change is −35 ppm/° C. and the frequency varies greatly in thetemperature range of −30° C. to +85° C. Therefore, it is necessary tolower the temperature coefficient of the frequency change.

Patent Document 1 (Japanese Patent Publication No. 2001-53579A)describes a device fabricated by bonding a SAW propagation substrate anda supporting substrate together with an organic thin film layer. Thepropagation substrate is a 30-μm-thick lithium tantalate substrate, forexample, and is bonded to a 300-μm-thick glass substrate with a15-μm-thick organic adhesive.

Patent document 2 (Japanese Patent Publication No. 2006-42008A)describes a SAW device fabricated by laminating a lithium tantalatesubstrate (125 μm in thickness) and a quartz glass substrate (125 μm inthickness) together with an adhesive. Specifically, according to (0030),an adhesive layer is required because the direct bonding of thesupporting substrate and the propagating substrate results in thepeeling and cracks.

Patent document 3 (Japanese Patent Publication No. Hei 06-326553A),Patent Document 4 (Japanese Patent No. 3774782B) and Patent document 5(U.S. Pat. No. 7,105,980B) also describe SAW devices fabricated bybonding a SAW propagation substrate and a supporting substrate together.

Further, according to Patent Document 6 (Japanese Patent Publication No.2005-229455A), oxidized layers of a thickness of 0.1 to 40 μm are formedon both main faces of a silicon supporting substrate, and apiezoelectric substrate is then bonded to the supporting substrate toproduce a SAW device. The oxidized layer of silicon is indispensable forreducing the warping of the thus obtained composite piezoelectricsubstrate 1.

According to the description of (0007) and (0013) of Patent Document 7(Japanese Patent publication No. 2002-135076A), the surface roughness ofthe substrate is 10 μm and it is difficult to make the thickness of anadhesive layer constant.

According to (0018) of Patent Document 8 (Japanese Patent PublicationNo. H09-167936A), even when the rotation angle θ, cutting angle, of apropagation substrate is varied, it is shown substantially sametemperature characteristics for the cases of, for example, 36° Y, 40° Y,42° Y and 44° Y.

According to FIG. 6 of Patent document 9 (Japanese Patent publicationNo. H02-37815A, it is shown dependency of temperature characteristics onthe electrode thickness. According to the description, the electrodethickness does not influence on the temperature dependency of frequency.

According to FIG. 4 of Patent document 10 (Japanese Patent PublicationNo. 2005-65160A), it is used quartz substrates having Euler angles of0°, 127° and 90° to show the relationship between standardized electrodethickness H/λ and TCF (frequency temperature coefficient) at 25° C.

The thermal expansion coefficient and Young's modulus of lithiumtantatate are described in (0021) of Patent document 11 (Japanese PatentPublication No. 2008-301066A).

Pages 43, 44, 36 and 37 of Non-Patent Document 1 “How-to; Strength ofMaterials: Basics” (authored by Hirofumi IDE and published by THE NIKKANKOGYO SHIMBUN, LTD.) describe the relationship of thermal expansioncoefficient and Young's Modulus of a bonding material.

Pages 989 and 991 of Non-Patent Document 2 “Science of Silicon” (editedby USC Semiconductor Basic Technique Research Group and published onJun. 28, 1996) describes the thermal expansion coefficient and Young'sModulus of silicon.

Non-Patent document 3 “Handbook of Glass Optics” (published by Asakurashoten on Feb. 28, 1963, page 792) describes data of borosilicate glass.

Patent document 12 (Japanese Patent Application No. 2009-40947: JapanesePatent publication No. 2009-278610A) relates to the present patentapplication.

RELATED TECHNICAL DOCUMENTS Non-Patent Documents

-   (Non-Patent Document 1)-   Pages 43, 44, 36 and 37 of “How-to; Strength of Materials; Basics”    authored by Hirofumi IDE and published by THE NIKKAN KOGYO SHIMBUN,    LTD.-   (Non-Patent Document 2)-   Pages 989 and 991 of “Science of Silicon” edited by USC    Semiconductor Basic Technique Research Group and published on Jun.    28, 1996-   (Non-Patent Document 3)-   “Handbook of Glass Optics” published by Asakura shoten on Feb. 28,    1963, page 792

Patent Documents

-   (Patent Document 1) Japanese Patent Publication No. 2001-53579A-   (Patent document 2) Japanese Patent Publication No. 2006-42008A-   (Patent document 3) Japanese Patent Publication No. Hei 06-326553A-   (Patent Document 4) Japanese Patent No. 3774782B-   (Patent document 5) U.S. Pat. No. 7,105,980B-   (Patent Document 6) Japanese Patent Publication No. 2005-229455A-   (Patent Document 7) Japanese Patent publication No. 2002-135076A-   (Patent Document 8) Japanese Patent Publication No. H09-167936A-   (Patent document 9) Japanese Patent publication No. H02-37815A    (Patent document 10) Japanese Patent Publication No. 2005-65160A-   (Patent document 11) Patent Publication 2008-301066A-   (Patent document 12) Japanese Patent Application No. 2009-40947    (Japanese Patent publication No. 2009-278610A)

SUMMARY OF THE INVENTION

In any of the aforementioned references, however, the problem of theshift of the passband due to temperature changes is not solved. Ifanything, they are moving away from the solution.

In paragraphs (0025) and (0037) of the Patent document 1, there is adescription of the temperature coefficient of frequency of the SAWdevice fabricated by bonding the lithium tantalate substrate to thesupporting substrate. The temperature characteristics of the device arehardly improved compared with those of SAW devices fabricated in alithium tantalite substrate only. For example, in the case of a 2-GHzSAW filter, a passband shift of ±4 MHz is observed in a temperaturerange of minus 30 to plus 85° C. This corresponds to ±7% of thenecessary bandwidth. Therefore, it is proved that the provision of theadhesive layer between the lithium tantalate propagation substrate andthe glass supporting substrate hardly improves the temperaturecharacteristics of frequency.

TABLE 1 propagation Propagation substrate substrate/ (bottom surfaceroughened/ adhesive layer/ adhesive layer/ glass substrate glasssubstrate Lithium tantalite −28 −30 36° Y substrate TemperatureCoefficient of frequency (ppm/° C.)

Although paragraph (0037) of the Patent document 2 includes thedescription that “it also becomes possible to improve the temperaturecharacteristics of frequency of the surface acoustic wave device”, nodata on the improvement is presented.

In paragraph (0062) of the Patent document 3 as well, a cleardescription is given that it is impossible to make practical use of amethod of bonding a surface acoustic wave propagation substrate to asupporting substrate.

Judging from the above, it is common knowledge that it is impossible tomake practical use of surface acoustic wave substrates having, forexample, a structure in which a lithium tantalate propagation substrateis bonded to a supporting substrate and that it is particularlyimpossible to lower the temperature coefficient of frequency.

Further, according to the Patent document 6, it is required to hold theSi substrate for several tens of hours while flowing oxygen gas under ahigh temperature of, for example, 1000° C. to form a surface oxidizedfilm. According to this process, however, in addition to the surfaceoxidation of the Si substrate, Si atoms themselves are dissolved intothe thus formed SiO₂ layer. This results in a defect layer of Si alongthe interface between the Si and SiO₂ layer that reduces the adhesivestrength along the interface. Moreover, the thickness of the adhesivelayer between the Si supporting substrate and the piezoelectricsubstrate is 3 μm in all the examples. In addition to this, it isdescribed that if the thickness of the adhesive layer would have beenless than 1.5 μm, the adhesive strength would be insufficient to resultin the peeling at 250° C. (0028).

An object of the present invention is to lower the temperaturecoefficient of frequency of a surface acoustic wave device including apiezoelectric single crystal propagation substrate.

The present invention provides a surface acoustic wave devicecomprising:

a supporting substrate;

a propagation substrate comprising a piezoelectric single crystal;

an organic adhesive layer having a thickness of 0.1 to 1.0 μm bondingthe supporting substrate and the propagation substrate; and

-   -   a surface acoustic wave filter or resonator provided on the        propagation substrate.

Contrary to the common knowledge of those skilled in the art, thepresent inventors have continued the study of structure in which apropagation substrate of a piezoelectric single crystal, for example, alithium tantalate single crystal, is bonded to a supporting substrate.Then, they attempted thinning the organic adhesive layer, which is anapproach that had been previously overlooked. The significance of suchan attempt had been denied in (see, for example, paragraph (0062) ofPatent document 3).

However, contrary to expectations, it has been found that thepropagation substrate is firmly bonded to the supporting substrate andthe temperature coefficient of frequency is considerably low. That is,in the case where the thickness of the organic adhesive layer was from0.1 to 1.0 μm, temperature characteristics brought about by thedifference in thermal expansion coefficients between the propagation andsupporting substrates were considerably improved. In contrast, in thecase where the thickness of the adhesive layer was over 1 μm, a stressresulting from the differences in thermal expansion coefficient betweenthe propagation and supporting substrates was absorbed by the organicadhesive, and therefore the effect of improving the temperaturecharacteristics could not be secured, if anything. Further, in the casewhere the thickness of the adhesive layer is below 0.1 μm, it seems thatthe temperature characteristics of frequency are deteriorated again dueto the influence of voids, and thus it has been confirmed that even ifthe adhesive layer is thinned as much as possible, the temperaturecharacteristics are not necessarily improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a), 1(b), 1(c), and 1(d), are schematic cross-sectional viewsof a laminated body for a surface acoustic wave device made in the orderof the manufacturing process.

FIG. 2( a) is a schematic cross-sectional view of a surface acousticwave device 6, and FIG. 2( b) is a schematic plan view of the surfaceacoustic wave device 6.

FIG. 3( a) is a plan view of a surface acoustic wave device with aresonator, and FIG. 3( b) is a cross-sectional view taken along lineA-A′ in FIG. 3( a).

FIG. 4 is a graph showing the relationship between thickness of adhesivelayers, thermal expansion coefficients, and the temperaturecharacteristics of frequency.

FIG. 5 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 6 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 7 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 8 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 9 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 10 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 11 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 12 is a graph showing the relationship of the thickness of anadhesive layer and the temperature characteristic of frequency.

FIG. 13 is a graph showing the temperature characteristics of frequencywhen a supporting substrate is made of silicon or borosilicate glass anda ratio of the thickness of the supporting substrate and that of apiezoelectric substrate is varied.

DETAILED DESCRIPTION OF THE INVENTION

The surface acoustic wave device according to the present inventionincludes a surface acoustic wave filter or a resonator. The surfaceacoustic wave filter is a bandpass filter as described later. Theresonator is a surface acoustic wave oscillator element, and includesone-port and two-port types.

In this invention, materials for a supporting substrate are preferablyselected from the group consisting of silicon, sapphire, aluminumnitride, alumina, borosilicate glass and quartz glass. Preferably, thesupporting substrate is made of silicon or borosilicate glass, and mostpreferably silicon. The use of these materials makes it possible toreduce the difference in thermal expansion with a propagation substrateand further improve the temperature characteristics of frequency.

Preferably, an oxide film is not formed on the surface of the supportingsubstrate. It is thus possible to improve the adhesive strength of thesupporting and propagation substrates and to prevent the peeling orcracks of the supporting and propagation substrates even at a hightemperature. On the viewpoint, the supporting substrate may preferablybe made of silicon without a silicon oxide film on the surface. Thepresence and absence of the surface oxide film can be observed using aTEM (transmission electron Microscope) at the cross section.

Furthermore, according to the invention, materials for the propagationsubstrate are preferably selected from the group consisting of lithiumniobate, lithium tantalate and lithium niobate-lithium tantalate solidsolution single crystals having high electromechanical couplingcoefficients. Preferably, the piezoelectric single crystal is lithiumtantalate.

Further, preferably, the direction of propagation of surface acousticwave in the propagating substrate is X direction and the cutting angleis rotation Y plate. More preferably, the propagating substrate is 36 to47° rotational Y cut plate.

Materials for the organic adhesive layer for bonding the supportingsubstrate and the propagation substrate are preferably, but not limitedto, an acrylic resin or an epoxy resin.

According to the invention, a thickness “t” of the organic adhesivelayer is set at 0.1 to 1.0 μm; in terms of the further improvement ofthe temperature characteristics of frequency of the surface acousticwave device, the thickness of the organic adhesive layer is preferably0.1 μm or more, or 0.8 μm or less.

FIG. 1 is schematic cross-sectional view of a laminated body for thesurface acoustic wave device made in the order of the manufacturingprocess.

As shown in FIG. 1( a), a supporting substrate 1 is prepared. As shownin FIG. 1( b), an organic adhesive 2 is applied onto a surface of thesupporting substrate 1 and as shown in FIG. 1( c), a substrate 3 of apiezoelectric single crystal is bonded to the adhesive layer 2. Then, asillustrated in FIG. 1( d), the substrate 3 is worked into a thin plate,i.e., a propagation substrate 3A having a thickness T2.

Thereafter, as shown in FIGS. 2( a) and 2(b), input electrodes 4 andoutput electrodes 5 are formed on the propagation substrate 3A to obtaina transversal surface acoustic wave device 6. Surface acoustic waves arepropagated from the input electrodes 4 to the output electrodes 5 asindicated by arrow 7. The portion where the propagation is madefunctions as a surface acoustic wave filter.

With surface acoustic wave filters for cellular phones, resonant typesurface acoustic devices are mainly used. FIGS. 3( a) and 3(b) show oneexample of such devices. FIG. 3( a) is a plan view of the electrodepattern of the surface acoustic wave device, and FIG. 3( b) is across-sectional view taken along line A-A′ in FIG. 3( a).

Electrodes 16, 17, and 18 are formed on a propagation substrate 10 toobtain a resonant surface acoustic wave device. In this example, thepropagation substrate 10 is bonded to a supporting substrate 12 via anorganic adhesive layer 14. The supporting substrate 12, the adhesivelayer 14, and the propagation substrate 10 are formed according to thepresent invention as described above.

The method for forming the organic adhesive layer is not limited; theutilization of printing and spin coating can be exemplified.

Materials for forming the surface acoustic wave filter and resonatorinclude aluminum, aluminum alloy, copper and gold, and may preferably bealuminum or aluminum alloy. Such aluminum alloy may have a compositionof 0.3 to 5 weight percents of Cu added to Al. In the alloy, Ti, Mg, Ni,Mo or Ta may be used instead of Cu.

The ratio (t/λ) of the thickness “t” of the surface acoustic wave filteror resonator with the wavelength “λ” of the surface acoustic wave filtermay preferably be 3 to 15 percent and more preferably be 5 percent andmore and 15 percent or less.

The thickness T1 of the supporting substrate 1 is preferably not lessthan 100 μm, more preferably not less than 150 μm, and most preferablynot less than 200 μm, from the viewpoint of the improvement of thetemperature characteristics. Further, from the viewpoint of theminiaturization of products, the thickness T1 is preferably not morethan 500 μm.

The thickness T2 of the propagation substrate 3A is preferably 10 to 50μm, more preferably 10 to 40 μm, and most preferably be 10 to 30 μm,from the viewpoint of the improvement of the temperature characteristicsof frequency.

EXAMPLES Example 1

The surface acoustic wave device 6 of FIG. 2 was made using themanufacturing method shown in FIG. 1.

It should be noted that, as the substrate 3 was used a 36° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thelinear expansion coefficient in the SAW propagation direction X was 16ppm/° C. As the supporting substrate 1, a single crystal siliconsubstrate was used. The linear expansion coefficient in the SAWpropagation direction X of the supporting substrate 1 was 3 ppm/° C. Thesupporting substrate 1 was formed with a thickness T1 of 350 μm, thepiezoelectric single crystal substrate 3 was formed with a thickness of350 μm, and both the substrates were bonded together with the organic(acrylic) adhesive at 180° C. Then, the thickness of the piezoelectricsingle crystal substrate 3 was reduced to 30 μm by lapping andpolishing. On the resulting propagation substrate 3A, the inputelectrodes 4 and output electrodes 5 of metallic aluminum were formed.(Thickness “t” of electrode)/(wavelength “λ” of surface acoustic wave)is 7 percent.

The thickness “t” of the organic adhesive layer 2 was changed variouslywithin the range of 0.05 to 15 μm. Then, the thermal expansioncoefficient of each surface acoustic wave device and the temperaturecoefficient of frequency at the resonance point were measured; theresults of the measurement are presented in Table 2 and FIG. 4.

TABLE 2 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 2 5 10 15Thermal Expansion 16 8 9 16 16 16 16 coefficient (ppm/° C.) Temperature−30 −15 −17 −30 −30 −30 −30 characteristics (ppm/° C.)

From these results, it can be seen that by setting the thickness of theorganic adhesive layer to 0.1 to 1.0 μm, the temperature coefficient offrequency is considerably and critically improved.

Example 2

Next, the surface acoustic wave device of FIG. 3 was made according tothe same procedure as the Example 1. The thus obtained device wassubjected to the same experiment as the Example 1 to prove that thetemperature coefficient of frequency is considerably and criticallyimproved by setting the thickness of the organic adhesive layer to 0.1to 1.0 μm.

Example 3

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 36° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 is made of silicon single crystal. The thickness“T1” of the supporting substrate 12 was 200 μm. The thickness of thepropagation substrate 10 was 30 μm. The electrodes 16, 17 and 18 made ofaluminum and having a thickness of 0.14 μm was formed on the propagationsubstrate 10. (Thickness “t” of electrode)/(wavelength “λ” of surfaceacoustic wave) is 7 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 5 and table 3.

TABLE 3 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 15Temperature coefficient of −30 −17 −18 −30 Frequency (ppm/° C.)

Example 4

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 47° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate 12 was 350 μm and thethickness of the propagation substrate 10 was 30 μm. The electrodes 16,17 and 18 made of aluminium and having a thickness of 0.14 μm was thenformed on the thus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 7 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 6 and table 4.

TABLE 4 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 15Temperature Coefficient of −31 −14 −16 −31 Frequency (ppm/° C.)

Example 5

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 47° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate 12 was 350 μm and thethickness of the propagation substrate 10 was 30 μm. The electrodes 16,17 and 18 made of aluminum alloy (Al-1% Cu) and having a thickness of0.14 μm was then formed on the thus obtained propagation substrate 10.(Thickness “t” of electrode)/(wavelength “λ” of surface acoustic wave)is 7 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 7 and table 5.

TABLE 5 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 15Temperature coefficient of −31 −14 −17 −31 Frequency (ppm/° C.)

Example 6

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 47° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate was 350 μm and the thicknessof the propagation substrate 10 was 30 μm. The electrodes 16, 17 and 18made of aluminum and having a thickness of 0.06 μm was then formed onthe thus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 3 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 8 and table 6.

TABLE 6 Thickness t of Organic adhesive layer (μm) 0.05 0.1 1 15Temperature coefficient of −30 −13 −16 −30 Frequency (ppm/° C.)

Example 7

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 47° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate was 350 μm and the thicknessof the propagation substrate 10 was 30 μm. The electrodes 16, 17 and 18made of aluminum and having a thickness of 0.3 μm was then formed on thethus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 15 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 9 and table 7.

TABLE 7 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 15Temperature Coefficient of −32 −16 −18 −32 Frequency (ppm/° C.)

Example 8

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 36° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate 12 was 500 μm and thethickness of the propagation substrate 10 was 10 μm. The electrodes 16,17 and 18 made of aluminum and having a thickness of 0.14 μm was thenformed on the thus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 7 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 10 and table 8.

TABLE 8 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 15Temperature coefficient of −30 −12 −12 −30 Frequency (ppm/° C.)

Example 9

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 36° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate 12 was 150 μm and thethickness of the propagation substrate was 25 μm. The electrodes 16, 17and 18 made of aluminum and having a thickness of 0.14 μm was thenformed on the thus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 7 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 11 and table 9.

TABLE 9 Thickness t of organic adhesive layer (μm) 0.05 0.1 1 15Temperature Coefficient of −32 −18 −20 −32 Frequency (ppm/° C.)

Example 10

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 36° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal. Thethickness “T1” of the supporting substrate 12 was 300 μm and thethickness of the propagation substrate was 40 μm. The electrodes 16, 17and 18 made of aluminum and having a thickness of 0.14 μm was thenformed on the thus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 7 percent.

The thickness “t” of the organic adhesive layer 2 was variously changedin a range of 0.05 to 15 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 12 and table 10.

TABLE 10 Thickness t of organic adhesive Layer (μm) 0.05 0.1 1 15Temperature coefficient of −32 −17 −18 −33 Temperature (ppm/° C.)

Example 11

The surface acoustic wave device of FIG. 3 was made using themanufacturing method shown in FIG. 1.

It is noted that, as the propagation substrate 10 was used a 36° Y-cut,X-propagation lithium tantalate substrate which had been cut out at anangle determined so as to form the rotated Y-cut plate and in which thedirection of SAW propagation was set at the direction of the X-axis. Thesupporting substrate 12 was made of silicon single crystal orborosilicate glass. The thickness of the propagation substrate was 30 μmand the thickness of the adhesive layer was 0.3 μm. The electrodes 16,17 and 18 made of aluminum and having a thickness of 0.14 μm was thenformed on the thus obtained propagation substrate 10. (Thickness “t” ofelectrode)/(wavelength “λ” of surface acoustic wave) is 7 percent.

The thickness “T1” of the supporting substrate 1 was variously changedin a range of 100 to 500 μm. The temperature coefficient of frequency atthe resonance point of the surface acoustic device was measured for eachdevice and the results were shown in FIG. 13 and table 11.

TABLE 11 Thickness of supporting substrate/ Thickness of piezoelectricsubstrate 3 7 10 13 16 Temperature Coefficient of −20 −18 −15 −13 −12Frequency (ppm/° C.) Silicon Temperature Coefficient of −22 −20 −18 −14−13 Frequency (ppm/° C.) Borosilicate glass

As can be seen from the results, when the silicon substrate is used andthe borosilicate glass substrate is used, the temperature coefficient offrequency was very low and substantially proportional with the ratio ofthe thickness of supporting substrate and that of the piezoelectricsubstrate, over a thickness of the supporting substrate of 100 to 500μm.

Example 12

The surface acoustic wave device 6 of FIG. 2 was made according to thesame procedure as the Example 1.

The following tests were performed under the same condition as theExample 1 except that the organic adhesive layer was made of epoxy resinadhesive. The thickness “t” of the organic adhesive layer 2 wasvariously changed in a range of 0.05 to 15 μm. The temperaturecoefficient of frequency at the resonance point of the surface acousticdevice was measured for each device to obtain the similar results as theExample 1.

Example 13

The thickness of the organic adhesive was changed and its relationshipwith the adhesive strength (compressive shearing) of the 36° Y cut Xpropagation lithium tantalite substrate and the silicon substrate. Thedimensions of the lithium tantalite substrate and the silicon substratewere 5×5×1 mm.

Thickness of organic adhesive: 0.02 μm

-   -   Adhesive strength: 25 kgf/cm²

Thickness of organic adhesive: 0.05 μm

-   -   Adhesive strength: 40 kgf/cm²

Thickness of organic adhesive: 0.1 μm

-   -   Adhesive strength: 100 kgf/cm²

Thickness of organic adhesive: 0.2 μm

-   -   Adhesive strength: 200 kgf/cm²

As can be seen form the above results, when the thickness of the organicadhesive layer is 0.1 μm or more, the target adhesive strength of 60kgf/cm² or higher can be successfully attained. It is further preferredthat the surface roughness of each adhesion surface of the lithiumtantalite substrate and the silicon substrate may preferably be 0.1 m orless.

The invention claimed is:
 1. A surface acoustic wave device comprising asurface acoustic wave filter or resonator, said device comprising: asupporting substrate; a propagation substrate comprising a piezoelectricsingle crystal; an organic adhesive layer having a thickness of 0.1 to1.0 μm and bonding the supporting substrate and the propagationsubstrate; and an electrode provided on the propagation substrate. 2.The device of claim 1, wherein the piezoelectric single crystal isselected from the group consisting of lithium niobate, lithium tantalateand lithium niobate-lithium tantalate solid solution.
 3. The device ofclaim 2, wherein the piezoelectric single crystal comprises lithiumtantalate.
 4. The device of claim 2, wherein a surface acoustic wavepropagates in the propagation substrate in X direction and wherein thepropagation substrate comprises 36 to 47° Y cut substrate.
 5. The deviceof claim 4, wherein said electrode comprises aluminum or an aluminumalloy.
 6. The device of claim 1, wherein a ratio “t/λ” of a thickness“t” of the electrode with respect to a wavelength “λ” of a surfaceacoustic wave is 3 to 15 percent.
 7. The device of claim 1, wherein thepropagation substrate has a thickness of 10 to 40 μm.
 8. The device ofclaim 1, wherein the supporting substrate has a thickness of 150 to 500μm.
 9. The device of claim 1, wherein the supporting substrate comprisesa material selected from the group consisting of silicon, sapphire,aluminum nitride, alumina, borosilicate glass and quartz glass.
 10. Thedevice of claim 9, wherein the supporting substrate comprises silicon orborosilicate glass.
 11. The device of claim 10, wherein the supportingsubstrate comprises silicon.
 12. The device of claim 1, wherein an oxidefilm is not formed on a surface of the supporting substrate.
 13. Thedevice of claim 3, wherein a surface acoustic wave propagates in thepropagation substrate in X direction and wherein the propagationsubstrate comprises 36 to 47° Y cut substrate.